Subdiffraction distances have been determined by exploiting quantum and near field properties of the interaction between light and matter in the nanometer scale.
For example, Fluorescence/Förster Resonance Energy Transfer (FRET) [1]}, [2]}, [3]}, [4]} has proven to be a valuable technique as it provides an optical signal directly related to the proximity of the molecules.
The desire to extend this technique to other biological systems with different time and length scales has been hindered by the inherent limitations of fluorescent dyes (i.e. lack of photostability, low brightness and short range of interaction).
Super resolution techniques such as STED [5]} or PALM [6]} have recently gained momentum to directly observe fluorescent molecules spaced closer than the diffraction limit.
Although much work has been done to increase the total acquisition time and frame rate, these methods are still limited by the lack of photostability and the need to image a single resolvable structure per diffraction limited spot at a time.
